Windows 10 - Application Starts but Window does not Maximize

I installed FireFox 43... and everything was working fine. Then, even though the browser was started (mouse over showed the open page's thumbnail image), the window itself would not maximize.

I went to the ridiculous extreme of uninstalling and reinstalling FireFox (using Revo - so I'm pretty sure that the uninstall cleaned up after itself) and I am still having the same issue - that is the browser starts but the window doesn't maximize. The browser doesn't shut down with the Close Window choice off the right click so I have to use Task Manager to shut it down.

I didn't love using Internet Explorer in earlier versions of Windows and I don't especially like Edge either. Firefox has been my browser choice for as long as it's been available and I still want to continue using it.

Any notion on why the window won't maximize and and/or how to fix it (without re-installing Windows or creating a new user account and starting all of the customization over again)?

The Following User Says Thank You to holdum333 For This Useful Post:

System is clean or so says Malwarebytes Anti-Malware and Sophos AntiVirus. It's the only app affected (so far).

After poking around on my laptop a bit (and reading some things suggested holdum333, I discovered that Revo did NOT completely remove FF from my system. I deleted the FireFox folder in my AppData and reinstalled. So far this worked. Now on the re-customizing FF - a chore, but not a big one.